Researchers help honeybees help themselves against a devastating parasite

UNC-Greensboro researchers try to harness honeybees' natural defense to help save them from the Varroa mite.

On the blueberry farm

BLADEN COUNTY — A blueberry farm is a unique place. Take a stroll through one and you'll find rows of bushes roughly 4-5 feet tall, weighed down by berries in varying shades of dark blue, red, yellow and orange.

Ralph Carter’s family has been farming blueberries like this on a patch of Bladen County farm in White Lake, NC for generations.

“It’s really neat to see all the changes through the years,” Carter says, walking through the rows of bushes. He pauses to say hello to all of the migrant workers who work on the farm for a few weeks every summer to help with the harvest. Some of the same workers return year after year before moving north to other farms.

“When my parents started the farm, it went from that road to that clump of trees back there,” Carter adds. “It’s grown a bit since then.”

There have been a lot of changes through the years. More acres were added; there's more machinery and technology to process the produce; and a large building near the farm holds all of the cleaning, sorting and packaging equipment. And there’s one other change: there are fewer bees to pollinate the blueberries.

The need for bees

“We really need to have the bees hit the plants four to six times to get the crop to normal size,” Carter says as he looks over a blueberry bush. “I’m just not sure the population really understands the importance of the bee and how much it touches our lives."

It’s the same story nationwide. Almost half of the bee colonies in the United States have been wiped out by a combination of habitat loss, pesticides, climate change and disease. So Carter rents thousands of bees from out of state for a few weeks in the spring to pollinate the bushes.

“We try to have an average of 2-2 1/2 hives per acre,” Carter explains. “That sounds like a lot, but the reason you want that many is that not every day is a good day; some are cool, some are rainy. So on days that are good days, you have more bees that can go out.”

The more bees, the better life is for most of us.

“One-third of all of the food that ends up on our table depends on the honeybee pollination, and that means fertilizing the flowers so they can actually fruit,” says Olav Rueppel, Ph.D. and biology professor at UNC-Greensboro. He and several students are opening the top of a beehive that is tucked into a back corner of campus.

“Somewhere in the middle of all this activity there is one queen and she can lay 2,000 eggs in one day,” explains Rueppel, who points out the queen bee moving through a mass of flying and crawling honeybees. In the hive, there are hundreds of male drones whose primary function is reproduction. There are also more than 20,000 female worker bees in the hive that forage for food, build combs and store honey for the winter.

Varroa mites

Researchers are searching for a practical, cost-effective and nontoxic approach to fighting infestations of varroa mites, a tiny parasite that is wiping out honeybee colonies worldwide.

“We are trying to harvest the natural defenses that honeybees have to improve their defenses and the defense of the hive to combat the mite,” says Rueppel.

You have to look closely to see a honeybee that is infected with a varroa mite. The mite appears as a small red bump on the back of the bee. It might seem small, but to a tiny bee, the mite is a physical burden. It would be the equivalent to a large dinner plate carried on the back of a human.

But the mite is more than a weight to carry around.

Varroa mites transmit viruses that can wipe out entire colonies. The mites reproduce by laying their eggs in the cells of a honeybee comb that are built for honeybee larvae.

“A varroa mite will go into a honeybee cell just before it is capped, and about two weeks later, the varroa will emerge with about five fertile offspring, as that developed honeybee emerges as an adult,” explains Kaira Wagoner, a post-doctoral student at UNC-Greensboro who is working with Professor Rueppel on the research program.

“So from a single cell that is infested with varroa, you can produce five more varroa, so you can see how the varroa population can build up quickly in the colony."

That exponential reproduction rate explains why just a few varroa mites can quickly wipe out a honeybee colony. So the key to stopping the infestation is to destroy the varroa mites before they exit the cells in the hive.

Helping honeybees help themselves

UNC-Greensboro researchers believe a special chemical could be the key to stopping varroa mite infestations.

It turns out that when the mites lay their eggs, the honeybee larvae give off a chemical signal to alert the nurse honeybees to the presence of mites. Nurse bees uncap the wax covering of the cell to check for mites and remove the mites if they are found. It’s called hygienic behavior.

UNC-Greensboro researchers want to better understand the chemical signals that trigger hygienic behavior. Because by developing a way to increase hygienic behavior, nurse bees could be encouraged to inspect cells and remove mite-infected larvae. The team is also researching whether the chemical trigger could be used to breed more disease-resistant hives.

The goal is to develop a way to help honeybees help themselves.

“And what that would mean is that bees can detect varroa mites that are inside these wax cells with these young bees, and parasitizing these young bees,” says Rueppel, “but then the bees would know how to uncap those cells and interrupt the mite life cycle. It would be a natural way to save the honeybee.”